Screen assemblies are used in vibratory separators to sort “oversized” particles from fluid or other particles. Screen assemblies include a wire or synthetic mesh screen cloth that is affixed to a frame. The frame is retained by the separator and product to be sorted is introduced to the top surface of the screen cloth. The combination of vibratory forces and product weight strains each wire in the screen cloth near the frame. Such strain varies from wire to wire around the edge of the screen assembly. Once a first wire yields or breaks under the strain, nearby wires are placed under greater strain and the break often widens across several wires.
Typically, screen assemblies used in vibratory separators have either steel, thermoset, or composite thermoplastic frames. The screen cloth is attached to a steel frame by spot welding or by using and adhesive. The screen cloth is attached to a thermoset frame by using an adhesive. For either attachment method, strain relief must be provided at the interface of the screen cloth and the frame when there is a large area of unsupported mesh. Typically, a bead of silicone or other caulking-type of elastomer bead is manually applied to the frame to provide strain relief to the screen cloth. However, the bond between silicone and steel is not always strong, resulting in pieces, or strings, of silicone breaking free from the frame and screen cloth to contaminate the product being processed by the vibratory separator. Silicone is chemically undesirable to many end users. Further, early screen failure can occur when individual wires in the area of the lost strain relief are subjected to strain and fatigue, causing them to break. The use of a silicone bead typically extends cure time and thereby manufacturing costs. In addition, application of the silicon bead to the frame is often performed manually, which results in an inconsistent bead size and variations in the amount of material used from screen to screen. Such inconsistency is often observed between screens manufactured by a single operator as well as between screens manufactured by different operators.
The screen cloth typically is attached to rigid composite thermoplastic frames by first heating the thermoplastic material and then pressing the mesh into the soft thermoplastic, which is allowed to cool. The current or existing composite frame includes an internal mesh support grid that divides the screening area into relatively small discreet zones. The zones are each small enough that a strain relief is not necessary at the interface of the mesh and the outer frame. However, the internal support grid utilizes valuable sorting area, leaving less area for processing.
It would be an improvement to the art to have a screen assembly wherein the frame includes a strain relief zone providing sufficient strain support to the screen cloth to eliminate the need for an internal grid to support the screen cloth, or if an internal grid is required, to provide strain support so that large mesh spans between ribs are feasible.
It would also be an improvement to the art to have a screen assembly that can be manufactured in a process that is repeatable by a single operator and reproducible by different operators. It would also be an improvement to have a screen that may be manufactured using automated equipment to further improve the consistency between screen assemblies. In addition to improving the quality of the screen assembly, the improved uniformity of screen assemblies would also result in a more predictable screen life. It would also be an improvement to have a screen that does not require the use of an adhesive or silicone which can take a relatively long time to cure during screen manufacturing.